The present invention relates generally to cardiac pacing devices and other types of implantable medical devices that can be programmed and/or analyzed following implantation using an external diagnostic/programmer system. Particularly, this invention relates to a patient activated telemetry control unit that uses a bidirectional link to communicate with implantable devices. More specifically, the patient control unit utilizes a bidirectional, asymmetric, dual-mode telemetry link, wherein in the first mode, the patient control unit transmits data at a high bit rate to the implanted device, and in the second mode, the patient control unit receives data at a low bit rate from the implanted device.
Implantable devices are implanted in a human or animal for the purpose of performing a desired function. This function may be purely observational or experimental in nature, such as monitoring certain body functions; or it may be therapeutic or regulatory in nature, such as providing critical electrical stimulation pulses to certain body tissue, nerves or organs for the purpose of causing a desired response. Implantable medical devices such as pacemakers, perform both observational and regulatory functions, i.e., they monitor the heart to ensure it beats at appropriate intervals; and if not, they cause an electrical stimulation pulse to be delivered to the heart in an attempt to force the heart to beat at an appropriate rate.
In order for an implantable device to perform its functions at minimum inconvenience and risk to the person or animal within whom it is used, a noninvasive telemetry means has been provided to allow data and commands to be easily passed back and forth between the implantable device and an external device. Such an external device, known by a variety of names, such as a controller, programmer, or monitor, provides a convenient mechanism through which the operation of the implantable device can be controlled and monitored, and through which data sensed or detected by the implantable device can be transferred out of the implantable device to an external (non-implanted) location where it can be read, interpreted, or otherwise used in a constructive manner.
As the sophistication of implantable devices has increased in recent years, emphasis on the amount of data that must be transferred between an implantable device and its accompanying external device or programmer, has dramatically increased. This, in turn, has resulted in a search for more efficient ways to effectuate such a data transfer at high speed. Such high speed data transfer typically increases the complexity and cost of the telemetry system, thus rendering the use of an additional patient controlled telemetry system an inefficient and impractical proposition.
Another challenge facing the implementation of a practical patient controlled telemetry system is the complexity and relatively high cost and large size of a patient controlled telemetry system that communicates with the implanted device.
While certain devices incorporate patient activation features by allowing the patients to provide input to the telemetry system, they add design complexity and cost. Some of these exemplary devices are described in the following patents.
U.S. Pat. No. 4,625,730 to Fountain et al., entitled xe2x80x9cPatient ECG Recording Control for an Automatic Implantable Defibrillationxe2x80x9d describes an implantable automatic defibrillator includes sensors which are placed on or near the patient""s heart to detect electrical signals indicative of the physiology of the heart. The signals are digitally converted and stored into a FIFO region of a RAM by operation of a direct memory access (DMA) controller. The DMA controller operates transparently with respect to the microprocessor which is part of the defibrillator. The implantable defibrillator includes a telemetry communications circuit for sending data outbound from the defibrillator to an external device (either a patient controller or a physician""s console or other) and a receiver for sensing at least an externally generated patient ECG recording command signal. The patient recording command signal is generated by the hand held patient controller. Upon detection of the patient ECG recording command, DMA copies the contents of the FIFO into a specific region of the RAM.
U.S. Pat. No. 4,884,575, entitled xe2x80x9cCardiac Pacer with Patient-Controlled Exercise Rate and Methodxe2x80x9d describes a cardiac pacemaker pulse generator adapted to generate electrical stimuli at a first pacing rate, and to selectively increase the rate to a second higher pacing rate. A timer triggers the rate increase to establish the higher rate as an exercise rate following the passage of a preset period of time after the timer is enabled. An external magnet controlled by the patient activates a reed switch to enable the timer to commence timing. The pulse generator is further adapted to respond to a second pass of the magnet over the reed switch after enabling of the timer to thereupon disable the timer before the preset period of time has expired. If the second pass of the magnet occurs after the exercise rate has begun, the element for increasing the rate is disabled to return the pulse generator to the lower pacing rate.
U.S. Pat. No. 5,490,862, entitled xe2x80x9cAtrial Defibrillator Having Patient Activated Modalityxe2x80x9d describes an implantable atrial defibrillator that includes a programming means responsive to a patient activated mode command, for causing the sequence initiating means to activate an intervention sequence means only in response to a sequence command, and an automatic mode command for causing the sequence initiating means to activate the intervention sequence means at predetermined times. The programming means is responsive to the patient activated mode command for causing the sequence initiating means to activate the intervention sequence means only in response to the sequence command generated from external to the patient and responsive to a combined automatic and patient activated mode command for causing the sequence initiating means to activate the intervention sequence means in response to the sequence command at predetermined times.
U.S. Pat. No. 5,752,976, titled xe2x80x9cWorld wide Patient Location and Data Telemetry System for Implantable Medical Devicesxe2x80x9d describes a method for communicating with an implanted medical device. The medical device includes a telemetry transceiver for communicating data and operating instructions between the implanted device and an external patient communications control device that is located in proximity to the patient within the implanted device transceiving range. The control device includes a patient activated link for permitting patient initiated personal communication with the medical support network. A system controller in the control device controls data and voice communications for selectively transmitting patient initiated personal communications and global positioning data to a medical support network.
U.S. Pat. No. 5,755,737, entitled xe2x80x9cMethod and Apparatus for Diagnosis and Treatment of Arrhythmiasxe2x80x9d describes an implantable anti-arrhythmia device with an associated patient activator. The patient is provided with an activator which informs the implanted device that the patient believes that anti-arrhythmia therapy is necessary. In response to receipt of the activation signal, the implanted device defines a time interval thereafter during which a second, less stringent set of arrhythmia detection criteria must be met, in response to which the device will deliver a cardioversion or defibrillation pulse.
One feature of the present invention is to satisfy the still unsatisfied need to improve the patient""s control of an implanted medical device and thus physiological condition, by providing the patient with a control unit which is small in size, relatively inexpensive, and simple to produce and to use. The patient activated telemetry control unit can be designed and implemented with minimal design changes to existing telemetry systems, and without significantly increasing the overall cost of the implanted device.
The patient control unit uses a bidirectional, asymmetric, dual-mode telemetry link, to communicate with the implantable device. In a first mode, the patient control unit transmits data at a high bit rate to the implanted device, and in the second mode, the patient control unit receives data at a low bit rate from the implanted device.
While in the second or receive mode, the patient activated telemetry control unit receives data at a low speed using a particular mode of operation of the implanted device. According to this mode of operation, each byte transmitted to the patient activated telemetry control unit is comprised of a predetermined number of identical bits, i.e., eight ones or eight zeros. The patient activated telemetry control unit recognizes each of the received bytes as a single bit, and the reception rate is therefore reduced to, for example, one eight. As a result of such a reduction in the reception bit rate, the hardware design and implementation of the patient activated telemetry control unit are greatly simplified and its cost reduced to within practical and affordable limits.